The field of art to which the present invention pertains includes check valves with disc-type closure elements pivotally mounted on a shaft for movement between open and closed positions in the valve's flow passage in response to fluid flow through the valve. The invention further relates to check valves of the aforementioned type wherein the discs are spring-biased towards their closed position, and wherein a resilient seat is provided to establish a leak-proof seal between the discs and the valve body when the valve is closed.
A great deal of effort has been directed towards improving disc-type check valves, most of which has been concentrated on the operation and sealing characteristics of the discs in the closed position, and upon their action while moving into that closed position. However, relatively little prior work has been done to solve the problems of wear and instability of the valve internals when under flowing conditions. Conventional flat discs are often unstable during flow through the valve, for at that time unbalanced forces exist due to varying service conditions. Although many designs and configurations of discs and other internal valve elements are known, none of these have overcome the aforementioned wear and stability problems that unduly shorten the useful life of these valves.
Another problem with check valves arises when back pressure is very low due to low fluid head on the downstream side of the valve. Under this condition many such valves leak because the back pressure is insufficient to create enough force to cause deformation of the resilient seat, especially where the seat has a relatively high seal area in order to adequately support the discs during high pressure conditions. Some check valves, such as the type described in Wheeler U.S. Pat. No. 3,074,427, issued Jan. 22, 1963, have resilient seats with beaded or other contoured configurations, but in these structures the seat deforms until metal-to-metal contact is established between the disc and the valve body, thereby greatly limiting the effectiveness of the seat in establishing a fluid-tight seal under all pressure conditions.